Myths come from an article published by Space.com
called The Top 5 Cosmic Myths. Some very interesting reading is
Myth 1: Meteors
are heated by friction as they pass through the atmosphere.
This one makes
sense, which is why it's so pernicious. But it's still wrong.
are tiny bits of dust, rock, ice or metal that have the
unfortunate luck of having their orbits intersect the Earth's.
When they pass through our atmosphere, they are heated so
ferociously that they glow (and at this point are called meteors),
and are visible for hundreds of miles.
However, it is not
friction that heats them. Think of it this way: a space
shuttle's tiles are extremely delicate; they crumble easily in
your hand. If they were heated by friction as the shuttle
de-orbits and enters the atmosphere at Mach 25, the tiles would
disintegrate. That's not a very good design characteristic.
In reality, it
isn't friction, but ram pressure that heats the
meteoroid. When a gas is compressed it gets hot, like when a
bicycle pump is vigorously used to inflate a tire. A meteoroid,
moving at 33,500 mph (15 kilometers a second) or more compresses
the air in front of it violently. The air itself gets very hot,
which is what heats the meteoroid. That's the fact, not
2: Meteors are still very hot when they hit the ground.
You'd expect that something
heated up so much that it glows would still be hot a couple of
minutes later. Actually, the situation is a bit more
The super-hot air
in front of the meteoroid is not actually in contact with the
particle. (A particle can still be referred to as a meteoroid as
it races through the atmosphere, while "meteor" is
meant to describe the whole glowing phenomenon.)
quick motion sets up a shock wave in the air, like from a
supersonic airplane. The shocked air sits in front of the
meteoroid, a few centimeters away (depending on the meteoroid's
size) in what's called a standoff shock. Between the shocked air
and the surface of the meteoroid is a relatively slow-moving
pocket of air.
The surface of the
meteoroid melts from the heat of the compressed gas in front of
it, and the air flowing over it blows off the melted portion in
a process called ablation. The meteoroid's high velocity
provides the energy for all this heat and light, which rob it of
speed. When it falls below the speed of sound, the shock wave
vanishes, the heating and ablation stop, and the meteoroid then
falls rather slowly, perhaps at a couple of hundred mph (or a
few hundred kilometers per hour).
It's still pretty
high up in the atmosphere at this point, and takes several
minutes to fall to the ground. Remember, this tiny bit of rock
spent a long time in space, and the core is pretty cold. Also,
the hottest parts were melted and blown off. Even more, the air
up there is cold, which chills the rock as well.
All of these things
together mean that not only is the rock not hot when it
hits the ground, it can actually be very cold. Some meteorites
(what a meteoroid is called after it impacts) have actually been
found covered in frost!
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